How Does an Egg Make an Organism

Lecture is presented by Sir John Bertrand Gurdon ,In 1962, Gurdon, then at Oxford University, announced that he had used the nucleus of fully differentiated adult intestinal cells to clone South African clawed frogs (Xenopus laevis).This was the first demonstration in animals that the nucleus of a differentiated somatic cell retains the potential to develop into all cell types (ie, is totipotent) and paved the way for future somatic cell nuclear transfer experiments, including the 1996 cloning of the sheep, Dolly.

Gurdon began cloning experiments using nonembryonic cells—specifically, cells from the intestinal lining of tadpoles. Gurdon believed that the tadpoles were old enough so that cells taken from them would be differentiated. Gurdon exposed a frog egg to ultraviolet light, which destroyed its nucleus. He then removed the nucleus from the tadpole intestinal cell and implanted it in the enucleated egg. The egg grew into a tadpole that was genetically identical to the DNA-donating tadpole. But the tadpoles cloned in Gurdon’s early experiments never survived to adulthood and scientists now believe that many of the cells used in these experiments may not have been differentiated cells after all. In later work, however, Gurdon successfully produced sexually mature adult frogs from eggs into which genetically marked nuclei had been transplanted from differentiated tadpole cells.

Gurdon’s experiments captured the attention of the scientific community and the tools and techniques he developed for nuclear transfer are still used today. The term clone (from the Greek word klōn, meaning “twig”) had already been in use since the beginning of the 20th century in reference to plants. In 1963 the British biologist J. B. S. Haldane, in describing Gurdon’s results, became one of the first to use the word clone in reference to animals.

In this Hitchcock lecture he explores the process of going from egg to organism.